Fan beam radiator



July 29, 1952 T. J. KEARY FAN BEAM RADIATOR Filed June 13, 1945 FIG! COUPLING PROBE ROTATING JOINT INVENTOR THOMAS JOSEPH KEARY Patented July 29, 1952 FAN BEAM RADIATOR Thomas Joseph Keary, Brockton, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application June 13, 1945, Serial No. 599,162 7 Claims. (01. 250-3353) This invention relates to directional microwave antennas for radio echo detection apparatus and more particularly to a waveguide-head feed for a micro-wave antenna to produce a radiation beam pattern which is very narrow in the horizontal plane, but wide in the vertical plane, such a pattern often being referred to as a fan beam.

For more eifective use of certain radio echo detection systems on ships at sea subject to rolling and pitching where no stabilization device is employed to assure that a directional pencil beam will be maintained in constant horizontal elevation it becomes necessary that the beam used have considerable width in the vertical plane so that it will continue to illuminate a surface target continuously during rolling of the ship. The L same requisite holds equally in the matter of reception. It is also desirable that the radiated energy be horizontally polarized, and also that minor lobes of the pattern be minimized. Like-' wise the system should have a minimum sensifeeding it which produces a horizontally polarized directional radiation beam'pattern with a main lobe very narrow in the horizontal plane but broad in the vertical plane.

. Another object is to provide an antenna system producing a fanned radiation beam pattern with very small minor lobes. V ,7

Another objectis to provide an antenna system .relatively insensitive to moderate variations in the transmitting frequency. c

It is another object of this invention to provide a truncated paraboloidal reflector and located substantially at the focus thereof a vertical wave guide terminated by a plane-reflector at an angle of about with the vertical and having in the side of said wave guide nearest the paraboloidal reflector an opening or window-through which reflected energy maypass to illuminate the main paraboloidal reflector whereby a radiation pattern may be produced having substantially only one lobe, said lobe being narrow in the horizontal plane and broad in the'yertical plane;

Other objects and features of the invention may be discovered from a consideration ofthe following detailed description together with the drawings. a

Fig. 1 is a perspective view of a typical embodiment of the invention showing the truncated paraboloidal 'main reflector and also the wave guidefeed; l

Fig. 2 is atop view of the embodiment shown in Fig. 1;.

Fig. 3 isa' side view of the embodiment shown in Fig. 1; and

Fig. 4 is a full view of the wave guide feed which shows the opening and window covering the same, and the. iris.

Considering now in detail the embodiment portrayed in the drawings, there appears a principal radiation reflector having the shape of a portion of a paraboloid or as it is sometimes called paraboloid of revolution. The portion used in this embodiment is taken in the region of the vertex which would be at point 2. Line 3 represents the location of the axis of the paraboloid. The reflector widths extend equally on either side of thevertex and equally above and below it. A more exact specification of the reflector shape here utilized may be had by considering that portion of a paraboloid which is included between two planes parallel to and substantially-equidistant from the axis and also included between two'planes perpendicular to the axis one of which planespasses through the vertex. It should be understood, however, that the reflector need not necessarily be cut, symmetrically about the vertex.

The reflector I is attached to a supporting arm 4 which also carries a section of wave guide 5 formed into a gooseneck 6. Electromagnetic energy is introduced into the wave guide 5 by. a vertical couplingprobe, the top of which appears at H in Fig, 3, which couples the, guide to a rotating joint, illustrated as a block 20,- so as .to excite it in the- TE mode. The energy-travels around the gooseneck 6 and through an iris 1 located within the wave guide and held between flange 8 at the top of the gooseneck 6 and a flange 9. The iris and two flanges are held together by bolts l0. Flange 9 is attached to and supports a shortverticalsection of the samesize rectangular wave guide; l-2 v wh ic h is terminated by a flat reflector plate -l 4 which is at an angle of substan; tially 45 with the direction of transmission of energy along theguide so as to reflect the energy in'the direction of the axis 3 of the main re {Iopermitthis reflectedenergy to pass towards the main reflector l a window 16' isfpro vided attachedbyscrews [Bio a flange H on-the;waye guide ",2 seve in a. rectangularropening 1, r min on the side toward the main reflector II The dimensions are so chosen that.- the T opening 3 covered by the window I6 is located substantially at the focus of the main reflector l.

Horizontally polarized energy passes from the opening covered by window 16 to the main reflector l and is reflected in a horizontally polarized beam having its direction of maximum radiation along the direction of the axis 3. The width of the beam in the horizontal plane is inversely dependent on the horizontal width of the main reflector I and the width of the beam in the vertical plane is inversely dependent on the vertical width of the main'reflector I. In the pesent case the beam will be therefore narrow in the horizontal plane and broad in the vertical plane. While the use of a main reflector such as reflector l is not new in the art it is believed that the particular type of feed embodied here is novel and it has proved very successful in tests.

The probe ll being vertical, the supporting arm 4 may be revolved about an axis coincident with the axis of the probe, and the rotating joint 20 permits the rotation of the whole assembly in azimuth successively to train the radiation beam in all directions to provide a continuous scanning of the horizontal plane.

- While a particular use and embodiment of the invention has been described and shown, other embodiments and applications are possible and therefore the invention is not deemed limited except insofar as necessitated by the state of the prior art and the spirit of the appended claims.

What is claimed is: v

l. A directional 'micro-wave antenna system comprising a principal reflector having the form of that portion of the surface 'of a paraboloid of revolution in the region of the vertex thereof which is included between two parallel planes substantially equidistant from the. axis of the paraboloid and which is also included between twoplane's perpendicular to the said axis, one of which passes through said vertex, and a rectangular wave guidehaving'as its termination a plane reflector positioned at an angle of substantially forty-five degrees with the energy transmision direction of the wave guide, said Wave guide having a window therein ajacent to said plane reflector and between said plane reflector and said principal reflector, said window being positioned substantially atthe focus of the paraboloi'dal reflector.

2. A directional micro-wave fan beam antenna system comprising a principal reflector having the form-of that portion of the surface of a paraboloid of revolution in the region of the vertex thereof which is included'between two parallel planes substantially equidistant from the axis' of the paraboloid and which is also-included between two planes ,perpendicular to the said axis, one of which passe's through said vertex, and a rectangular wave g'uide'adapted to transmit horizontally palarized 'electro-magnetic energy and terminated by a plane reflectoiy'said .wave guide also having a {window in the wall thereof facing the principal reflector, said wave guide being' positioned with" reference to said principal reflectonso that said window is substantially 'at the focus of said principalreflector.

3. A directional micro-wave fan beamantenna system comprising a" principal reflector having the form orthat portion of the surface of' a paraboloid "of revolutioni'i-n the region 'of the vertexthereofwhich isf'i'ncluded between two parallel planessubstantially equidistant-fromtl ie axis of the paraboloid and which is'also included between two planes perpendicular to the said axis, one of which passes through said vertex, a rectangular wave guide adapted to transmit horizontally polarized electro-magnetic energy and terminated by a plane reflector, said wave guide also having a window in the wall thereof facing the principal reflector, said wave guide being positioned with reference to said principal reflector so that said window is substantially at the focus of said principal reflector and an iris near the end of and within said wave guide for matching purposes.

4. A directional microwave antenna system for providing a radiation pattern which is narrow in the horizontal plane and broad in the vertical plane, comprising, a reflector having the form of that portion of a paraboloid of revolution in the region of the vertex thereof which is included between two parallel, horizontal planes substantially equidistant from the axis of said paraboloid and between two planes perpendicular to said axis, one of which latter planes passes through said vertex, a rectangular wave guide terminating in a plane reflector disposed at an angle of 45 to the axis of said wave guide, said rectangular wave guide having an opening formed in a narrow wall thereof adjacent said plane reflector and disposed between said plane reflector and said paraboloid, whereby said paraboloid may be illuminated by horizontally polarized energy from said rectangular wave guide.

5. A directional microwave fan beam antenna system comprising, a principal reflector having the form of that portion of the surface of a paraboloid of revolution in the region of the vertex thereof which is included between two parallel planes substantially equidistant from the axis of the paraboloid and which is also included between two planes perpendicular to the said axis, one of which passes through said vertex, a first section of rectangular wave guide terminated atone end in a first rectangular flange and adapted to transmit horizontally polarized electromagnetic energy, a second section of rectangular wave guide terminated at one end in a second rectangular flange and terminated at the other-end bya plane reflector inclined at an angle of 45 to the longitudinal axis of said sectionv and normal to the broad walls thereof, an

'iris' positioned between said first and second flanges, means securing said flanges and iris together, said second section of wave guide having an opening formed in the narrow'wall there of opposite said plane reflector and facing said principal reflector, and means supporting said principal reflector and said sections of wave guide to position said opening substantially at the focus of said principal reflector.

6. A directional microwave antenna system for providing a radiation pattern which is narrow in-the horizontal plane and broad in the vertical plane comprising, a reflector having the form of aportion of a pa'raboloidof revolution and having a finite focus, a first section of rectangular waveguide terminated atone end in' 'a first rectangular flange, a second section of similar rectangular wave guide terminated at one end in a 'second rectangular flange and at the other end ina-piane reflector inclined at an angle of 45 to the'longitudinal 'axisfof said section and normal to-the broad walls thereof, a'rectangular iris positioned between'said' flrst and second flanges and extending around the perimeter of said wave guide sections, means securing said flanges and the iris therebetween together, said second section of wave guide having an opening formed in the narrow wall thereof opposite said plane reflector, a window adapted to transmit electromagnetic energy secured across said opening, and means supporting said reflector and said sections of wave guide to position said opening substantially at the focus of and facing said paraboloid, said rectangular wave guide sections being adapted to transmit electromagnetic energy in the TE mode whereby said paraboloid 'is illuminated by horizontally polarized energy from said opening.

7. A directional microwave antenna system for providing a radiation pattern which is narrow in the horizontal plane and broad in the vertical plane comprising, a reflector having the form of a portion of a paraboloid of revolution and having a finite focus, a first section of rectangular wave guide adapted to be energized with electromagnetic energy in the TE mode, a second section of similar rectangular wave guide, said sections being axially joined together by cooperating rectangular flanges secured to adjacent ends of said sections, an iris positioned between said flanges and extending around the perimeter of said wave guide, the unsecured end of said second wave guide section being terminated in a plane reflector inclined at an angle of 45 to the longitudinal axis of said second section of wave guide and normalto the broad walls thereof, said second section of wave guide having a rectangular opening formed in the narrow vwall thereof opposite from said plane reflector, a third rectangular flange secured to said wave guide and surrounding said opening, a window adapted to transmit electromagnetic energy secured to said third flange and closing said opening, and means supporting said reflector and said wave guide sections to position said opening substantially at the focus of and facing said paraboloid, whereby said paraboloid is illuminated by horizontally polarized energy from said opening.

THOMAS JOSEPH KEARY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Bureau of Standards Scientific Papers N0. 469, part of vol, 19, Directive Radio Transmission on a Wave Length of 10 Meters, by Dunmore and Engel, April 11, 1923. 

